Identification of flow regimes and dispersion pathways around in-line cylinders

Abstract

Flow and dispersion over in-line cylinders have received considerably less attention compared to those around isolated cylindrical obstacles in the fluid dynamics literature and within cuboid-delimited street canyons in the urban boundary-layer context. This investigation reveals that tank canyons share similar flow characteristics with street canyons while demonstrating distinct features. The flow regime transition from isolated to wake interference and skimming with respect to the canyon aspect ratio ($AR$), well established for urban canyons, is preserved in the case of tank canyons; however, turbulent flux exchanges across the canyon side open boundaries are more pronounced in the latter, attributed to reinforced flow encirclement around the cylindrical obstacles and enhanced horseshoe vortices. Dispersion pathways, in particular the centre-of-mass translation and mean tracer ages (${\tau }_a$), closely align with the flow regime. The overall monotonic increase in ${\tau }_a$ with $AR$, alongside a notable ($\sim 30\text{\%}$) decrease in the mean canyon circulation timescale ($T_c$), offers useful insights for the parameterisation of key timescales associated with flow and ventilation in cylinder-delimited canyons. Knowledge of the microenvironments within tank canyons is vital for integrating complex petrochemical plants into urban topographies, constituting an integral part of urban micrometeorological systems.